Standard keyboards for data-entry of text include an array of momentary switches, usually in 4 rows and 10 or 12 columns, with the center of each key usually spaced about 3/4 inches away from its neighbors. Almost all full-sized keyboards are arranged in the QWERTY pattern originating with Shole's (1860) patent, except for keyboards made for a small following of Dvorak's (1936) patent.
The conventional keyboard is designed for use by people with two hands on full-sized typewriters. When adapted for use by one-handed persons, or miniaturized, this type of keyboard does not perform well.
In miniaturized keyboards in use with text-based calculators and pocket computers, the keys and their spacing are reduced to about 1/2 inch or less, resulting in the operator's speed of typing being greatly diminished. The operator of such a keyboard loses the advantageous use of 8 or 9 fingers and primarily utilizes only the memory of where particular letters are located. This accounts for the popularity of miniature keyboards in which the letters are arranged alphabetically.
In the prior art, the only principal to switch-array keyboards is chording keyboards. For chording keyboards, fingers must operate in parallel or simultaneously for each signal sent. Two patents relating to this type of keyboard are Volnak (U.S. Pat. No. 4,467,321) for a 10-key chording keyboard, and Enfield & Rainey (U.S. Pat. No. 4,443,789), for a 6-key chording keyboard with mnemonic coding.
The history of typewriting has seen several patents on multiple-character-per-key keyboards, for example, Hesh (U.S. Pat. No. 2,532,228), Samuel (U.S. Pat. No. 3,633,724) and Zapp (U.S. Pat. No. 4,081,068). These patents are in the field of full-sized two-handed keyboards, and furthermore use lateral motion of the fingers. Kroczynski (U.S. Pat. No. 4,517,424) describes a hand-held control device which uses non-lateral motions, but does not describe any system for typing or text entry.
Finally, the instant invention relates to pocket-sized devices with full-screen displays. Lapeyre's (U.S. Pat. No. 4,324,976) appears to be directed to rear-facing keyboards. The instant device, however, can be attached to the side of a display.